1. Field of the Invention
This invention relates to a waveguide optical system, and more particularly to a waveguide optical system suitable for use with a high-density recording optical head or the like.
2. Description of the Prior Art
A high-density recording optical head utilizing a waveguide optical system is proposed in U.S. Pat. No. 4,425,023, etc. An example of such optical head is shown in FIG. 1(A) of the accompanying drawings. In FIG. 1(A), reference numeral 1 designates a substrate, reference numeral 2 denotes a light waveguide, reference numerals 3 and 4 designate prism light couplers, reference numeral 5 denotes a comb-shaped electrode, reference numeral 6 designates a condensing lens, and reference numeral 7 denotes a recording medium. A collimated laser beam 8 is directed into the light waveguide 2 by the inputting prism light coupler 3, is deflected by an elastic surface wave 9 created by the comb-shaped electrode 5 and emerges from the outputting prism light coupler 4. The emergent light beam 10 forms a spot 13 on the surface of the recording medium 7 by the condensing lens 6. Usually, with respect to the distribution intensity of the emergent light beam 10, the distribution of intensity in direction Y shown in FIG. 1(A) (the direction Y is parallel to a plane defined by the waveguide 2 and is perpendicular to an advancing direction of the emergent light beam 10) does not differ from the distribution of intensity of the input light beam 8, but as shown in FIG. 2 of the accompanying drawings, the distribution of intensity 15 of the emergent light beam 10 as seen from a plane XZ (along a direction Zr perpendicular to a direction Xr which is an advancing direction of the emergent light beam and lying in the plane XZ; also see FIG. 1B) becomes approximate to a distribution in which one side attenuates by an exponential function (the direction Z is parallel to the plane defined by the waveguide 2 and perpendicular to the direction Y and the direction X is perpendicular to the directions Y and Z). FIG. 3(A) of the accompanying drawings shows the distribution of amplitude of the emergent light beam in a case where, for example, LiNbO.sub.3 having Ti diffused therein is used as a light wwaveguide and a TiO.sub. 2 prism light coupler is provided on the light waveguide and He-Ne laser light of a width of 6 mm having a Gaussian distribution is caused to enter the light coupler. In this manner, one of the directions has a Gaussian distribution and the other direction has a one side exponential function distribution.
Now, generally, with regard to a recording light spot formed by a high-density recording optical head, to concentrate the energy density of light and enable high-density recording to be accomplished, the following conditions are required:
(1) that the spot size is very small; PA0 (2) that the peak value of the distribution of intensity of light in the spot is high; and PA0 (3) that the shape of the spot is substantially circular.
However, the distribution of intensity of the spot formed by condensing the emergent light beam by the conventional waveguide optical system whose three-dimensional distribution of amplitude is as shown in FIG. 3(A) by the use of the condensing lens 6 shown in FIG. 1 differs between the Y direction and the Zr direction, as shown in FIG. 3(B) of the accompanying drawings, and the waveguide optical system as shown in FIG. 1(A) suffers from a problem that it does not satisfy the conditions required as the high-density recording light spot.
Such a problem exists irrespective of the deflection of the light beam by a deflecting means, such as a comb-shaped electrode.